New state of matter in one-dimensional quantum gas

一维量子气体中物质的新状态

by Stanford University

斯坦福大学

Credit: CC0 Public Domain

信用：CC0公共领域

As the story goes, the Greek mathematician and tinkerer Archimedes came across an invention while traveling through ancient Egypt that would later bear his name. It was a machine consisting of a screw housed inside a hollow tube that trapped and drew water upon rotation. Now, researchers led by Stanford University physicist Benjamin Lev have developed a quantum version of Archimedes' screw that, instead of water, hauls fragile collections of gas atoms to higher and higher energy states without collapsing. Their discovery is detailed in a paper published Jan. 14in Science.

随着故事的发展，希腊数学家和修补匠阿基米德在穿越古埃及时遇到了一项发明，后来以他的名字命名。这是一台机器，由一个装在空心管内的螺钉组成，该空心管在旋转时捕获并吸水。现在，由斯坦福大学物理学家本杰明·列夫（Benjamin Lev）领导的研究人员开发出了阿基米德螺杆的量子版本，该螺杆代替水将脆弱的气体原子集牵引到越来越高的能态而不会塌陷。 1月14日在《科学》杂志上发表的一篇论文中详细介绍了他们的发现。

"My expectation for our system was that the stability of the gas would only shift a little," said Lev, who is an associate professor of applied physics and of physics in the School of Humanities and Sciences at Stanford. "I did not expect that I would see a dramatic, complete stabilization of it. That was beyond my wildest conception."

斯坦福大学人文与科学学院应用物理学和物理学副教授列夫说：“我对我们的系统的期望是气体的稳定性只会发生一点变化。” “我没想到我会看到它的戏剧性，完全稳定。这超出了我最疯狂的构想。”

Along the way, the researchers also observed the development of scar states— extremely rare trajectories of particles in an otherwise chaotic quantum system in which the particles repeatedly retrace their steps like tracks overlapping in the woods. Scar states are of particular interest because they may offer a protected refuge for information encoded in a quantum system. The existence of scar states within a quantum system with many interacting particles—known as a quantum many-body system—has only recently been confirmed. The Stanford experiment is the first example of the scar state in a many-body quantum gas and only the second ever real-world sighting of the phenomenon.

在研究过程中，研究人员还观察到了疤痕状态的发展，这种情况是粒子在极其混乱的量子系统中极为罕见的轨迹，在这种量子系统中，粒子反复地回溯其步伐，就像在树林中重叠的轨迹一样。疤痕状态特别令人感兴趣，因为它们可以为量子系统中编码的信息提供受保护的避难所。直到最近才确认具有多个相互作用粒子的量子系统中存在的疤痕状态（称为量子多体系统）。斯坦福大学的实验是多体量子气体中疤痕状态的第一个例子，而在现实世界中仅第二次看到该现象。

Super and stable

超级稳定

Lev specializes in experiments that extend our understanding of how different parts of a quantum many-body system settle into the same temperature or thermal equilibrium. This is an exciting area of investigation because resisting this so-called "thermalization" is key to creating stable quantum systems that could power new technologies, such as quantum computers.

Lev专门从事实验，这些实验扩展了我们对量子多体系统的不同部分如何沉降到相同温度或热平衡的理解。这是一个令人兴奋的研究领域，因为抵制这种所谓的“热化”是创建稳定的量子系统的关键，该系统可以为新技术提供动力，例如量子计算机。

In this experiment, the team explored what would happen if they tweaked a very unusual many-body experimental system, called a super Tonks-Girardeau gas. These are highly excited one-dimensional quantum gases—atoms in a gaseous state that are confined to a single line of movement—that have been tuned in such a way that their atoms develop extremely strong attractive forces to one another. What's super about them is that, even under extreme forces, they theoretically should not collapse into a ball-like mass (like normal attractive gases will). However, in practice, they do collapse because of experimental imperfections. Lev, who has a penchant for the strongly magnetic element dysprosium, wondered what would happen if he and his students created a super Tonks-Girardeau gas with dysprosium atoms and  altered their magnetic orientations 'just so.' Perhaps they would resist collapse just a little bit better than nonmagnetic gases?

在这个实验中，研究小组探索了如果调整一个非常不寻常的多体实验系统（称为超级唐克斯-吉拉多气体）会发生什么。这些是高度激发的一维量子气体（一种处于气态的原子，仅局限在一条运动线上），其调谐方式使它们的原子彼此产生极强的吸引力。它们的优点在于，即使在极端力的作用下，它们在理论上也不应坍塌成球形（就像正常的吸引气体一样）。但是，实际上，由于实验的不完善，它们的确会崩溃。对强磁性元素有兴趣的列夫（Lev）想知道，如果他和他的学生用with原子创建超级的唐克斯-吉拉多（Tonks-Girardeau）气体，并且“如此改变”它们的磁取向，将会发生什么。也许它们会比非磁性气体更好地抵抗崩溃？

"The magnetic interactions we were able to add were very weak compared to the attractive interactions already present in the gas. So, our expectations were that not much would change. We thought it would still collapse, just not quite so readily." said Lev, who is also a member of Stanford Ginzton Lab and Q-FARM. "Wow, were we wrong."

“与气体中已经存在的有吸引力的相互作用相比，我们能够添加的磁性相互作用非常弱。因此，我们的期望是不会有太大变化。我们认为它仍然会崩溃，只是不太容易。”列夫说，他也是斯坦福·金兹顿实验室和Q-FARM的成员。 “哇，我们错了吗？”

Their dysprosium variation ended up producing a super Tonks-Girardeau gas that remained stable no matter what. The researchers flipped the atomic gas between the attractive and repulsive conditions, elevating or "screwing" the system to higher and higher energy states, but the atoms still didn't collapse.

他们的变化最终产生了无论如何都保持稳定的超级Tonks-Girardeau气体。研究人员在吸引和排斥条件之间翻转了原子气体，将系统提升或“旋动”到越来越高的能量状态，但是原子仍然没有崩溃。

Building from the foundation

从基础建设

While there are no immediate practical applications of their discovery, the Lev lab and their colleagues are developing the science necessary to power that quantum technology revolution that many predict is coming. For now, said Lev, the physics of quantum many-body systems out of equilibrium remain consistently surprising.

尽管他们的发现没有立即的实际应用，但Lev实验室及其同事正在开发必要的科学，以推动许多人预言的量子技术革命。列夫说，目前，不平衡的量子多体系统的物理学始终令人惊讶。

"There's no textbook yet on the shelf that you can pull off to tell you how to build your own quantum factory," he said. "If you compare quantum science to where we

他说：“书架上还没有教科书可供您介绍如何建立自己的量子工厂。” “如果将量子科学与我们的研究进行比较

were when we discovered what we needed to know to build chemical plants, say, it's like we're doing the late 19th-century work right now."

是当我们发现建造化工厂所需的知识时，例如，这就像我们现在正在做19世纪晚期的工作一样。”

These researchers are only beginning to examine the many questions they have about their quantum Archimedes' screw, including how to mathematically describe these scar states and if the system does thermalize—which it must eventually—how it goes about doing that. More immediately, they plan to measure the momentum of the atoms in the scar states to begin to develop a solid theory about why their system behaves the way it does.

这些研究人员才刚刚开始研究关于量子阿基米德螺杆的许多问题，包括如何以数学方式描述这些疤痕状态以及系统是否确实热化（最终必须这样做）如何进行。更直接地，他们计划测量疤痕状态下原子的动量，以开始发展关于其系统为何如此行为的可靠理论。

The results of this experiment were so unanticipated that Lev says he can't strongly predict what new knowledge will come from deeper inspection of the quantum Archimedes' screw. But that, he points out, is perhaps experimentalism at its best.

这个实验的结果是出乎意料的，以至于列夫说，他无法强有力地预测，对量子阿基米德螺杆的更深入检查将带来什么新知识。但他指出，这也许是最好的实验主义。

"This is one of the few times in my life where I've actually worked on an experiment that was truly experimental and not a demonstration of existing theory. I didn't know what the answer would be beforehand," said Lev. "Then we found something that was truly new and unexpected and that makes me say, 'Yay experimentalists!'"

列夫说：“这是我一生中几次真正从事实验的实验之一，而不是对现有理论的真实证明。我不知道答案是什么。” “然后，我们发现了一些真正新的和出乎意料的东西，这让我说，是的实验主义者！'”

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 来源于：phys